The present invention relates to a measuring instrument installation on a process circuit that can be subjected to a medium under high pressure with a locking element between the measuring instrument, particularly in the form of a pressure transmitter, and the process circuit to test the imperviousness of the process circuit, and also relates to the removal of such a measuring instrument installation.
Mainly those measuring instrument installations are considered here which are used in processes with gaseous or liquid process media under high pressure in operation. In addition, the disclosure is centered on processes in which high pressures are built up e.g. in the cryogenic technology with fluid/gas change-overs.
A measuring instrument installation on a high-pressure process circuit is generally installed in such manner that a locking element that can be actuated as a pressure transmitter is installed between the process circuit and the measuring instrument.
For safety reasons, in particular for the removal of a measuring instrument or of a pressure transmitter when the process circuit is under pressure, it is a generally known measure to build up such a locking element by means of three valves in a so-called xe2x80x9cdouble blocking-and-bleedxe2x80x9d arrangement. For this purpose a valve is used on the side of the process circuit, the sealing seat of which is reinforced in the closing direction by the pressure on the side of the process circuit. In addition a valve is installed in the opposite direction on the measuring instrument side, so that the pressure prevailing in the measuring instrument or in the pressure transmitter reinforces this valve seat in the sealing direction. The two valves represent the xe2x80x9cdouble blockingxe2x80x9d arrangement. A third valve is installed in a xe2x80x9cTxe2x80x9d arrangement as a relief/bleed valve in the xe2x80x9cbleedxe2x80x9d function between these two valves. Before removing a measuring instrument or a pressure transmitter, the two first-mentioned valves are closed and the circuit between these valves is then relieved by means of the relief/bleed valve so that secure uncoupling is ensured of the segment of the high-pressure process circuit which must be opened when a measuring instrument is removed.
The installation of such an arrangement is expensive and requires relatively much space.
Furthermore a ball valve used as a stop valve is generally known, with a valve body as a ball housing, with a process circuit connection and a measuring instrument connection as well as with a ball in the ball housing that can be rotated between a pass position and a stop position. The ball is located between two ball seats, each with a sliding sleeve that is spring-loaded in direction of the ball and capable of sealed displacement and each with packing pressed in a ring-shaped manner against the ball. As a result a ball space is formed between the packings that is not directly sealed off from the process circuit connection and the measuring instrument connection. A ball seat arrangement of this type, with two spring-loaded ball seats or sliding sleeves with packings provides an extensively leak-free seal in a known manner, in particular, in case of pressure and temperature fluctuations. Due to the spring pressure, ball and seat wear is reduced, in particular, in case of pressure fluctuations and pressure surges.
It is furthermore known that the ball can be provided with a ball bore which provides a connection between the ball chamber and the process side when the ball valve is closed, so that pressure equalization takes place, especially with process media with great volume expansion.
It is an object of the present invention to develop a measuring instrument installation described herein above in such manner that, while the double blocking-and-bleed function is maintained, a considerably simpler, less expensive and space-saving arrangement becomes possible.
It is furthermore the object of the invention to provide a suitable process for the removal of a measuring instrument when using the measuring installation according to the invention.
These objects are attained by the invention with regard to the measuring instrument installation and with regard to the process.
According to a first aspect of the invention, the locking element is a ball valve with a valve body as a ball housing, with a process circuit connection and a measuring instrument connection as well as with a ball in the ball housing which can be twisted between a pass position and a lock position, said ball being provided with a passage bore that can be placed in the pass position. Furthermore two ball seats lying in the direction of the process circuit connection and two lying in the direction of the measuring instrument connection are provided, each with a sliding sleeve spring-loaded and sealed in the direction of the ball, each with a packing pressed in a ring-shaped manner against the ball. This creates a ball space between the packings which is not directly sealed off against the high-pressure zones, but at the same time the medium is able to enter this ball space under high pressure through leakage at the two sealing seats as well as during the locking process.
Furthermore the ball housing is provided with a passage to the environment as a relief/bleed connection in the area of this ball space to which a relief/bleed valve is connected.
The two spring-loaded ball seats can be regarded as two locking elements acting independently from each other in the sense of the initially mentioned xe2x80x9cdouble blockingxe2x80x9d function, since they seal off the corresponding connections from the ball on the process circuit side and on the measuring instrument side and from the ball space between these when in prescribed position.
The ball space between these ball seats acting in a xe2x80x9cdouble blockingxe2x80x9d function can now be connected to the environment according to the invention via a relief/bleed valve, so that the xe2x80x9cbleedxe2x80x9d function is possible for relief and/or bleeding.
In all, a xe2x80x9cdouble blocking-and-bleedxe2x80x9d function is created thereby in a very advantageous manner in a very compact, economical and technically safe and effective solution.
The measuring instrument installations with the characteristics described and claimed herein are advantageous and high-performing variations in design.
In a second aspect of the invention, a relief/bleed valve is included in form of a needle valve that can be screwed in, by means of which a relief and/or imperviousness test can be carried out in a very dosed manner.
The sliding sleeves are simply sealed by means of O-rings according to a third aspect of the invention whereby the sliding sleeves are spring-loaded in an advantageous manner by means of Belleville washers.
Still another aspect relates to the solution according to the invention in connection with a ball valve with straight circuit passage, so that the required geometrical conditions are advantageous. In principle however, it is also possible according to the invention to use a valve with a non-straight passage, e.g., a corner valve.
In yet another aspect, a ball valve can be used with conventional square wrench actuation.
Easy assembly of a ball valve is possible as an additional feature of the invention.
In still a further aspect, the invention is a process for the testing of imperviousness and for the removal of a measuring instrument, in particular of a pressure transmitter when the process circuit is subjected to high pressure in a measuring instrument installation as described in the foregoing aspects of the invention. In this case the following process steps must be carried out:
a) Closing the ball valve by rotating the ball into its locked position. As a result, the xe2x80x9cdouble-blockingxe2x80x9d functions with respect to the high pressure on the process circuit side and the measuring instrument side are established simultaneously in one step.
b) In a second process step, the relief/bleed valve, preferably in form of a needle valve, is opened at least partially. An imperviousness test of the two ball seats on the one hand, and on the other hand a relief of the ball space are effected thereby. If the ball seats are tight, at most a brief escape of medium takes place. In case of a gaseous medium this can be detected through a brief hissing sound. Thereby the xe2x80x9cdouble blocking-and-bleedxe2x80x9d function and reliable separation of the measuring instrument connection from the high-pressure process circuit are ensured.
c) In this way the measuring device, in particular a pressure transmitter, can be removed in a further process step without safety risk.